The invention relates to a pneumatic shock absorber comprising a cylinder, a piston mounted in the cylinder and arranged so that its piston rod extends out of the cylinder, a check valve forming an inlet port via which a pressure space delimited by the piston may be connected with an external source of fluid under pressure and an outlet valve to let off air compressed during damping motion of the pneumatic shock absorber.
An increase in the productivity of a machine is often something taking place in step with an increase in the speed of the drives used therein. Even pneumatic drives presently reach speeds as high as 3 m/s and more. In order to keep violent impacts, noise or vibration within reasonable limits, long familiar methods of energy conversion have been used in order to convert energy in the terminal drive positions by terminal damping or by hydraulic shock absorbers and in addition pneumatic shock absorbers have been employed, more especially in those cases in which for reasons of system geometry a pneumatic damping means is not able to be integrated in the pneumatic linear actuator. The advantages of a pneumatic shock absorber are to be seen more especially in a low weight, in the possibility of use at high stroke frequencies and the insensitivity to an increase in the operating temperature. Furthermore it is possible to achieve a gentler start of the damping effect. Unlike a hydraulic shock absorber it may also be used without any disadvantages in the foodstuffs industry and in medical appliances, since such a pneumatic shock absorber does not cause contamination. The rate of energy conversion is substantially higher than in the case of a hydraulic shock absorber.
A pneumatic shock absorber described in the German unexamined specification 2,730,860 of the initially mentioned type has an inlet check valve and an adjustable outlet excess pressure valve. This is partly necessary in order to let off compressed air when there is a pressure surge in the pressure space with the intention of preventing recoil from the terminal abutment and furthermore such an excess pressure valve precludes loss of the compressed air flowing in via the check valve in the unloaded condition. In order to adapt to different impact energies or masses to be retarded the initial pressure in the pressure space may be adjusted. Since the outlet valve always opens at a certain set pressure value such opening takes place at a higher pressure substantially earlier than is the case with a lower initial pressure. Thus the damping characteristic depends in an undesired manner to a great extent on the initial pressure which has been set. It is naturally possible to use the set screw in the piston rod to adjust the opening pressure value of the outlet valve. However, if the initial pressure is to be frequently changed this becomes a very inconvenient task and takes up much time. A further disadvantage is to be seen in the fact that the outlet valve requires a very stiff valve spring, more especially when the initial pressure is very high or the masses to be damped are very large. The result of this is that a very high residual pressure still acts on the piston in the retracted position, such pressure remaining after the outlet valve has closed again.